The three following proposed standards of the American National Standards Institute (ANSI) are hereby incorporated by reference.
xe2x80x9cFibre Channel Switch Fabric (FC-SW),xe2x80x9d rev 3.3, NCITS working draft proposed, American National Standard for Information Technology, Oct. 21, 1997;
xe2x80x9cFibre Channel Physical And Signaling Interface (FC-PH),xe2x80x9d rev 4.3 X3 working draft proposed, American National Standard for Information Systems, June 1, 1994; and
xe2x80x9cSCSI Fibre Channel Protocolxe2x80x94Second Revision (FCP-2),xe2x80x9d NCITS proposed draft, Dec. 21, 1999.
This invention relates to a method and apparatus for path determination in a storage area network (SAN). More particular this invention relates to selecting a path of a plurality of paths by a switch or switches connecting a host system to a storage system.
In the 1970""s and 1980""s various methods were developed for sharing storage between multiple computer servers, i.e., hosts. One such system was developed by U.S. Pat. No. 4,455,605, Cormier et al, filed Jul. 23, 1981 (herein referenced as Cormier). Cormier describes a path group having a plurality of communication paths between a host and the storage system. The communication paths were connection oriented and unless, the data traffic was continuous, there were numerous disconnections and reconnections to maintain good path utilization. In addition the selection of the path group was done by the host. While the redundancy in paths between the host and the storage system increases reliability, problems occurred in a heterogeneous operating system environment, for example, Windows, Mac, UNIX. Each host with its associated operating system would require a different implementation to determine the path group for that host""s operating system.
In the 1990""s performance improvements in storage and processors along with the move to distributed architectures such as client/server led to data intensive and high-speed network applications. This led to the development of storage area networks (SAN""s) which connected one or more servers to one or more storage systems via a Fibre Channel Fabric having one or more switches. The protocol is described in ANSI drafts FC-HW and FC-SW which are incorporated by reference. The Fiber Channel Protocol includes both copper and optical cable with speeds up to a few gigabits per second. While Fiber Channel has point to point service (Class 1), of primary use for SAN""s is connectionless service (Classes 2 and 3). Connectionless service uses frames, like for example, network packets, which allow a high data transfer rate.
FIG. 1 shows an example of a Storage Area Network. The Fibre Channel Fabric 12 includes one or more Fibre Channel switches 14, for example, xe2x80x9cSilkwormxe2x80x9d switches from Brocade Communications Systems, Inc., or xe2x80x9cSANboxxe2x80x9d switches from Ancor Communications, Inc The fabric connects one or more computer server systems 20, 22 with one or more storage systems 30, 32, 34. Each storage system could be, for example, a Redundant Array of Independent Disks (RAID), Direct Access Storage Device (DASD), tape backup, a CD-ROM library, or JBOD (Just a Bunch of Disks).
Fibre Channel switches such as from Brocade and Ancor provide fault tolerance due to switch failure as well as auto-discovery of end nodes, for example storage systems and hosts. If multiple switches are configured as a mesh or Ancor""s Multistage(trademark) Cross-connect, then the fabric should function at normal or near normal capacity with a switch failure. However, this addresses a small subset of path failures between source, e.g., server 20, and destination, e.g., RAID 30, systems. An example failure would be a port failure due to loss of reliable communications on a link from that port. In addition the change in path for frames due to load balancing is not addressed.
Thus there is a need for a more comprehensive, but simple, technique to change a path due to path failure or to provide for better path utilization, for example, by load balancing.
The present invention relates generally to a Fibre Channel Fabric determining an alternative path from a plurality of predetermined paths between a server system and a storage system in a Storage Area Network, where the Fibre Channel Fabric, includes one or more Fibre Channel switches.
An exemplary embodiment, provides a method for selecting a path from a plurality of pre-determined paths between a computer system and a storage system in a Storage Area Network, wherein the computer system and the storage system are connected together by one or more Fibre Channel switches. The method includes, establishing a first path from the plurality of predetermined paths between the computer system and the storage system. Next, a status of the first path is determined by the Fibre Channel switch or switches; and a second path from the plurality of pre-determined paths is selected based on the status of the first path. The selection by the Fibre Channel switch is independent of the computer system. The status could be, for example, a first path failure, such as a loss of reliable communications on a link of the first path, or a first path usage above a threshold.
In a second embodiment of the present invention a system for selecting an alternate path from a path group having a plurality of Fibre Channel paths in a Storage Area Network is provided. The system includes, a host, having a processor and a memory; a switch, including a processor and a memory, coupled to the host by a Fibre Channel path. The switch memory stores a data structure having the path group for determining the alternate path; and a storage system, including at least one logical volume, coupled to the switch by at least two Fibre Channel paths. In addition the switch may select the alternate path when an established path between the switch and storage system fails or when an established path between the switch and storage system has a usage above a pre-determined threshold.
In another embodiment of the present invention a Fibre Channel network device for connecting a host computer system to a storage system is provided. The network device includes: a plurality of ports belonging to a path group, where a first port in the path group receives the information designated for a second port in the path group, when there is a status change in the first port; a processor; and a memory having software operated on by the processor, the software including a table having the plurality of ports and the path group. The change in status may be, for example, a high usage of the first port or a first port failure.
A further understanding of the nature and advantages of the inventions herein may be realized by reference to the remaining portions of the specification and the attached drawings.